Lead Frame Based, Over-Molded Semiconductor Package with Integrated Through Hole Technology (THT) Heat Spreader Pin(s) and Associated Method of Manufacturing

ABSTRACT

A method and apparatus are provided for manufacturing a lead frame based, over-molded semiconductor package ( 7 ) with an exposed pad or power die flag ( 70 ) having multiple integrated THT heat spreader pins ( 71 ) configured for insertion into one or more vias ( 77 ) formed in a printed circuit board ( 78 ). The through hole heat spreader pins ( 71 ) may be formed as an integral part of the exposed pad ( 52 ) or may be solidly connected with the exposed pad ( 62 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to lead frame based semiconductor packages and amethod of manufacturing the same. In one aspect, the present inventionrelates to a lead frame based over-molded semiconductor package with anexposed pad having an improved electrical and thermal path within thepackage as well as within the completed assembly of package and printedcircuit board (PCB) or any other substrate material.

2. Description of the Related Art

Semiconductor packages with exposed pad (i.e., PQFN, QFN, HSOP, SOIC,QFP, TQFP, MO-188 etc.) provide a thermal path within the package toconduct heat from the integrated circuit die to the printed circuitboard (PCB). After PCB assembly, the highest thermal resistance valueswithin the intended heat path are induced by the thermal vias of PCBwhich lead through the PCB onto the PCB backside where a large copperplane acts as a heat sink. Thermal resistivity of the heat path can alsobe increased by typical assembly issues, such as solder voiding. Asshown in U.S. Patent Application Publication No. 2005/0110137,conventional approaches for dissipating heat do not address the issue ofthe high thermal resistivity generated by the thermal vias of the PCB.

Accordingly, a need exists for a semiconductor packaging apparatus andprocess which reduces the thermal resistance values within the intendedheat path. In addition, a need exists for a packaging device andmethodology which reduces the heat path from the die attach pad to thepackage outside. There is also a need for device packaging that avoidsthe process and performance limitations associated with typical assemblyissues during the packaging process. In addition, there is a need forimproved semiconductor processes and devices to overcome the problems inthe art, such as outlined above. Further limitations and disadvantagesof conventional processes and technologies will become apparent to oneof skill in the art after reviewing the remainder of the presentapplication with reference to the drawings and detailed descriptionwhich follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be understood, and its numerous objects,features and advantages obtained, when the following detaileddescription is considered in conjunction with the following drawings, inwhich:

FIG. 1 illustrates a diagonal view of the bottom of an example bodystructure of an exposed pad having an integrated THT heat spreader pin.

FIG. 2 illustrates a bottom view of an example package assembly with asingle THT pin body structure.

FIG. 3 illustrates a diagonal view of the bottom of an alternativeexample body structure of an exposed pad having a plurality ofintegrated THT heat spreader pins.

FIG. 4 illustrates a bottom view of an example package assembly with abody structure with multiple THT pins.

FIG. 5 illustrates a side view of a multi-pin body structure inaccordance with various embodiments of the present invention.

FIG. 6 illustrates a side view of a multi-pin body structure inaccordance with various alternative embodiments of the presentinvention.

FIG. 7 illustrates a cross section where a package with an exposed padhaving multiple integrated THT heat spreader pins is mounted onto aprinted circuit board.

FIG. 8 is a diagram showing the manufacturing process for a package inaccordance with various embodiments of the present invention.

FIG. 9 is a diagram showing various manufacturing process steps whichmay be used for a package in accordance with various embodiments of thepresent invention.

It will be appreciated that for simplicity and clarity of illustration,elements illustrated in the drawings have not necessarily been drawn toscale. For example, the dimensions of some of the elements areexaggerated relative to other elements for purposes of promoting andimproving clarity and understanding. Further, where consideredappropriate, reference numerals have been repeated among the drawings torepresent corresponding or analogous elements.

DETAILED DESCRIPTION

A method and apparatus are described for packaging a semiconductordevice using a lead frame-based over-molded semiconductor package withone or more through hole technology (THT) heat spreader pin(s) on anexposed pad as a direct electrical and heat path having reducedresistance. By integrally forming or attaching the heat spreader pin(s)to an exposed die pad, a direct and short electrical and heat path isprovided from the die attach pad to the package outside. The THT heatspreader pins may be manufactured in the lead frame manufacturingprocess, or may be pre-formed ahead of the actual package manufacturingprocess.

Various illustrative embodiments of the present invention will now bedescribed in detail with reference to the accompanying figures. Whilevarious details are set forth in the following description, it will beappreciated that the present invention may be practiced without thesespecific details, and that numerous implementation-specific decisionsmay be made to the invention described herein to achieve the devicedesigner's specific goals, such as compliance with process technology ordesign-related constraints, which will vary from one implementation toanother. While such a development effort might be complex andtime-consuming, it would nevertheless be a routine undertaking for thoseof ordinary skill in the art having the benefit of this disclosure. Forexample, selected aspects are depicted with reference to simplifiedcross sectional drawings without including every feature or geometry inorder to avoid limiting or obscuring the present invention. It is alsonoted that, throughout this detailed description, certain examplepackaging structures are depicted which may be formed using any desiredmanufacturing techniques for etching, milling, punching, machining orotherwise forming such structures at appropriate dimensions and sizes.Such details are well known and not considered necessary to teach oneskilled in the art of how to make or use the present invention.

FIG. 1 illustrates a diagonal view of the bottom of an example bodystructure 1 of an exposed pad or lead frame 10 having an integrated THTheat spreader pin 12. The lead frame 10 is basically the substrate or“back bone” carrier of a package. The lead frame 10 is typicallymetallic and conductive, although not always so. The lead frame 10includes a die flag which carries semiconductor chips. In accordancewith selected embodiments, the surface of the exposed pad 10 includesone or more through hole technology heat spreader(s) 12. While FIG. 2shows a single cylindrical-shaped pin structure 12 protruding from thesurface of the package, it will be appreciated that other shapes may beused for the pin structure 12, so long as the pin structure(s) protrudesufficiently away from the surface of the exposed pad 10 to permitphysical engagement and contact with the PCB vias (as describedhereinbelow). Whatever shape is used, the through hole heat spreader pin12 may be formed as an integral part of the exposed pad 10 so that it ismanufactured in one part with the exposed pad 10. For example, the padand THT pin could be integrally manufactured using etching, milling,punching or other machining procedures during the lead framemanufacturing process. Alternatively, the THT pin 12 may be manufacturedseparately from the pad 10 and then attached or connected with theexposed pad, such as by adding or inserting the THT pin 12 to the leadframe structure after manufacturing the lead frame body or pad 10 withpress fit, cold welding, or other suitable connection techniques. Theway in which the THT pins(s) 12 are produced could be of any appropriatetype for the various embodiments of the present invention describedherein.

Referring now to FIG. 2, a bottom view is illustrated of an examplepower quad flat pack no-lead (PQFN) package assembly 2 with a single THTpin body structure 22. The depicted package is shown with a number oflead frame components or other devices and connectors 26. In addition,the package is shown with an exposed pad 20 featuring one integrated THTheat spreader pin 22 which protrudes from the surface of the exposed pad20 as previously indicated in other embodiments and drawings.

Referring to FIG. 3, a diagonal view is illustrated of the bottom of analternative example body structure 3 of an exposed pad or lead frame 30having a plurality of integrated THT heat spreader pins 32, 34. Asillustrated, the THT pins are arranged in rows (e.g., pin row 34) andcolumns (e.g., pin column 32) which define a regular grid pattern. FIG.3 shows three rows and six columns of THT pins forming a grid pattern,though it will be appreciated that other patterns may also be used.Again, the pattern or grid of THT pins 32, 34 can be formed integrallywith the exposed pad 30 or subsequently by inserting or attaching thepins 32, 34 to the pad 30.

FIG. 4 illustrates a bottom view of an example PQFN package with a bodystructure having multiple THT pins 42, 48. The depicted package is shownwith a number of lead frame components or other devices and connectors46. As illustrated, the package is shown with an exposed pad 40featuring a plurality integrated THT heat spreader pin 42, 48 whichprotrude from the surface of the exposed pad 40 as previously indicatedin other embodiments and drawings.

FIG. 5 illustrates a side view of a multi-pin body structure 5 inaccordance with various embodiments of the present invention wherein oneor more THT heat spreader pins 52 are manufactured as an integral partof the exposed pad 50 during lead frame manufacturing. As depicted, eachintegrally formed pin 52 protrudes or extends perpendicularly from thepad 50, though other protrusion angles can be used, such as when thepins are configured for insertion into PCB vias having non-standardconfigurations. Accordingly, other shapes of for the THT pins 52 willprovide the same advantages and this invention. In accordance withvarious alternative embodiments of the present invention, FIG. 6illustrates a side view of a multi-pin body structure 6 wherein the THTheat spreader pins 62 are manufactured separately and inserted into theexposed pad 60. For example, during lead frame manufacturing of the pad60, one or mounting holes 64 are formed in the exposed pad 60.Subsequently, THT heat spreader pins 62 are inserted into the mountingholes 64 using any desired attachment or connection technique forsolidly connecting the pins 62 and pad 60.

FIG. 7 illustrates a cross section of a PQFN lead frame package 7 withan exposed pad or power die flag 70 having multiple integrated THT heatspreader pins 71 assembled on a printed circuit board 78. Though notdepicted, the pins 71 may be formed in rows and columns as previouslydescribed. The depicted package 7 includes one or more input/output(I/O) pads 74, an integrated circuit 73 (e.g., power die), a lead frame70 and die attach material 72 (e.g., solder, conductive epoxy or anyother applicable adhesive material) connecting the power die 73 to thelead frame 70. These elements are encased in mold compound 75 which istypically in the form of an epoxy compound or any other appropriatematerial that is applied to encase the power die 73, I/O pads 74 andpower die flag 70 as illustrated, leaving exposed the bottom of the pads70, 74 and the THT heat spreader pins 71 (which were either integrallyformed with the power die flag 70 or subsequently fixedly attachedthereto). The mold compound encapsulated package may then attached tothe printed circuit board (PCB) 78 by applying a solder joint 76 betweenthe PCB 78 and any device placed thereon, and then inserting the THTheat spreader pins 71 into via openings 77 formed in the PCB 78. Asillustrated, the PCB 78 includes a PCB conductor layer 79 formed at apredetermined thickness (e.g., approximately 0.35 microns of copper) onthe surfaces of the PCB vias 77, as well as on the top and bottomsurface of the PCB 78. Each via 77 has a predetermined width (e.g.,approximately 0.5 mm diameter) that is wider that the width of the THTpin 71 (e.g., approximately 0.4 mm pin diameter), and the THT pin length(e.g., approximately 1.5 mm) may be selected so that the pin 71 contactsthe conductor layer 79 in the via 77 and extends completely through thevia 77. Of course, it will be appreciated that other thickness, widthand length dimensions can be used, depending on the pin configurationand packaging type.

In the embodiment shown in FIG. 7, the upper surface of the die flag isdisposed in contact with the integrated circuit die to transfer heatgenerated at the integrated circuit die directly to the THT heatspreader pins 71, which in turn directly transfer the heat to the PCBvias 77 and copper plane 79. In this way, the trough hole heat spreaderpins 71 provide the package with a built-in, optimized heat path to thePCB 78 after assembly which increases on-board performance by increasingthe thermal performance (e.g. by up to at least a factor of three)compared to state-of-the-art assembly technologies. In addition, mostpotential board attach-related issues which may limit the packageon-board performance are eliminated. Also, the heat spreader pins 71provide a self-alignment benefit during PCB assembly. Because the heatspreader pins 71 reduce the thermal resistance of the heat path betweenthe die 73 and the PCB copper plane 79, the lead frame 70 may be usedwith power applications to attach a power die 73 to the PCB 78.

FIG. 8 is a flow chart diagram showing an example process 80 formanufacturing a package in accordance with various embodiments of thepresent invention. As a preliminary step, one or more heat spreader pinsare integrally formed in an exposed pad of a lead frame by etching,milling, punching, machining or otherwise forming the THT pins as anintegral part of the pad (81). For packages with etched lead frames, theheat spreader pins may be readily manufactured since the etchingprocesses used to manufacture the lead frames can be used to pattern theTHT pin(s) on the surface of the exposed pad without having additionalsteps to the overall process. Alternatively, the heat spreader pins maybe separately formed and attached by manufacturing the lead frame toinclude mounting holes (82) and then inserting separately-formed THTpins to the lead frame (83), such as by attaching, connecting, pressfitting, cold welding, or otherwise coupling the pins to the lead frame.

The various components to be connected to the lead frame may then beattached on the upper surface of the lead frame. These components willtypically be those which form part of a package that is to be moldencapsulated to some degree or another. The exact nature of thecomponents will depend on the device and the ultimate use of theresulting package (84). A mold compound is then applied to the variouscomponents of the package (85). This process can be carried out invarious different ways, including mold pressing or other mold compoundapplication methods. The package is then completed as appropriate forthe use required. This may include removal of some of the mold compoundfrom certain areas for connections, addition of leads, etc. to beincluded (86). The package is then attached to a PCB or other deviceusing a soldering process (87). The presence of the THT heat spreaderpins allows the package to be aligned with the PCB vias.

The manufacturing process of the package may include further steps thatare common place in the environment of manufacturing a semiconductorpackage. FIG. 9 shows an example sequence of manufacturing process stepswhich may be used for a package in accordance with various embodimentsof the present invention, though it will be appreciated that there aremany other variations. As depicted in FIG. 9, a single lead frame or aset (i.e. matrix) of lead frames 90/92 is manufactured and patternedwith one or more THT heat spreader pins 93 formed on the exposed padsthereof (150). After mounting the wafer, one or more different siliconwafers are split into single semiconductor dies by sawing or otherappropriate means and are inspected (152).

After die solder paste or any other appropriate die attach material (94)is applied (154), the semiconductor die(s) 95 is/are placed into the dieattach material 94, and then cured or reflowed. A de-flux and DI-Waterrinse step may then be carried out (156). If required, an epoxy or anyother appropriate die attach material is applied (158), and additionalsemiconductor dies are placed into the die attach material and/or a dieattach cure is carried out (160). A tape (96) is attached to the leadframes (162) to provide a support panel, wire bonds (99) are applied(164), and a visual check is carried out (166).

A molding compound (100) is applied (168) and the tape 96 is removed(170) to separate the support panel. A post mold cure (172) and lasermarking (174) steps are followed by a cleaning stage (176). The packageis then split into individual elements (178) and inspected (180).

In one form there is provided herein a method of manufacturing asemiconductor package by mounting an integrated circuit die on anexposed pad that includes one or more heat spreader structures on anexposed first surface of the exposed pad. The heat spreader structuresmay be formed from any heat conducting material, such as copper, and maybe formed as an integral part of the exposed pad using any desiredtechnique, such as etching, milling, punching or machining a lead frame.Alternatively, the heat spreader structures may be formed separatelyfrom the exposed pad by forming an exposed pad having with at least onemounting hole formed in the exposed first surface, forming one or moreheat spreader pins, and then affixing the heat spreader pins into themounting hole of the exposed pad so that the first heat spreader pinprotrudes from the exposed pad. In the method, an integrated circuit dieis affixed to a surface of the exposed pad opposite the exposed firstsurface, and then the integrated circuit die and exposed pad are encasedin a compound, leaving exposed the exposed first surface and first heatspreader structure. Next, the first heat spreader structure is attachedto a printed circuit board, such as by inserting the heat spreaderstructure through a via formed in the printed circuit board.

In another form, there is provided a lead frame-based, over-moldedsemiconductor package with an exposed pad. The exposed pad includes oneor more through hole technology heat spreader pins configured forinsertion into a via formed in a printed circuit board, where the heatspreader pins may be formed as an integral part of the exposed pad, ormay be formed separately from the exposed pad for subsequent fixedattachment to the exposed pad. In this way, heat spreader pins may beformed as part of any desired semiconductor package, including but notlimited to PQFN, QFN, HSOP, SOIC, QFP, TQFP or MO-188 packages. In aselected embodiment, the exposed pad and heat spreader pin may be formedwith copper, though any material that is electrically and thermallyconductive may be used.

In yet another form, there is disclosed an electronic device, such as apower quad flat pack no-lead (PQFN) package assembly structure, thatincludes a die that is at least partially encapsulated in a moldstructure. In addition, a die attach pad coupled to the die includes afirst surface exposed from the mold structure and one or more(integrally or separately formed) first through hole technology heatspreader pins protruding from the first surface. For example, where themold structure has a first bottom surface, the heat spreader pin and thefirst surface of the die attach pad are disposed in the mold structureto be exposed from the first surface of the mold structure. When a heatsink is disposed in thermal communication with the heat spreader pin ofthe die attach pad, heat from the die is thermally coupled to the pinand may be transferred to the heat sink.

Although the described exemplary embodiments disclosed herein aredirected to various lead frame based semiconductor package structuresand methods for making same, the present invention is not necessarilylimited to the example embodiments which illustrate inventive aspects ofthe present invention that are applicable to a wide variety of processesand/or devices. Thus, the particular embodiments disclosed above areillustrative only and should not be taken as limitations upon thepresent invention, as the invention may be modified and practiced indifferent but equivalent manners apparent to those skilled in the arthaving the benefit of the teachings herein. For example, FIG. 7 does notshow all the details of connections between various elements of thepackage, but it will be appreciated the leads, vias, bonds and otherconnection means can be used to effect any electrical connection.Similarly, other insulating materials can be used to electricallyisolate various components. Also, any combination of devices, pads,dies, etc. can be used as required for the desired package. Accordingly,the foregoing description is not intended to limit the invention to theparticular form set forth, but on the contrary, is intended to coversuch alternatives, modifications and equivalents as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims so that those skilled in the art should understand that they canmake various changes, substitutions and alterations without departingfrom the spirit and scope of the invention in its broadest form.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. For example, thedisclosed lead frame based semiconductor package structures provide anoptimized thermal path within the package by reducing thermal resistancevalues within the intended heat path through the PCB onto the PCBbackside (which features a large copper plane acting as a heat sink) byinserting a heat conducting or spreading pin structure into the thermalvias of PCB. In addition, typical assembly issues (i.e., solder voiding)which may limit the package on-board performance can be eliminated, andthe heat spreader pins allow the package and PCB to be self-alignedduring PCB assembly. However, the benefits, advantages, solutions toproblems, and any element(s) that may cause any benefit, advantage, orsolution to occur or become more pronounced are not to be construed as acritical, required, or essential feature or element of any or all theclaims. As used herein, the terms “comprises,” “comprising,” or anyother variation thereof, are intended to cover a non-exclusiveinclusion, such that a process, method, article, or apparatus thatcomprises a list of elements does not include only those elements butmay include other elements not expressly listed or inherent to suchprocess, method, article, or apparatus.

1-9. (canceled)
 10. A lead frame-based, over-molded semiconductorpackage with an exposed pad comprising at least one THT heat spreaderpin configured for insertion into a via formed in a printed circuitboard.
 11. The semiconductor package of claim 10, where said THT heatspreader pin comprises a plurality of heat spreader pins.
 12. Thesemiconductor package of claim 10, where said THT heat spreader pin isformed as an integral part of the exposed pad.
 13. The semiconductorpackage of claim 10, where said THT heat spreader pin is formedseparately from the exposed pad and is attached to the exposed pad. 14.The semiconductor package of claim 10, where the over-moldedsemiconductor package comprises a PQFN, QFN, HSOP, SOIC, QFP, TQFP orMO-188 package.
 15. The semiconductor package of claim 10, where saidexposed pad and THT heat spreader pin comprise copper.
 16. An electronicdevice comprising a package structure comprising: a mold structure; adie disposed within the mold structure; and a die attach pad coupled tothe die, said die attach pad comprising a first surface exposed from themold structure and at least a first through hole technology heatspreader pin protruding from the first surface.
 17. The electronicdevice of claim 16, wherein the mold structure has a first surface, andwhere the first through hole technology heat spreader pin and the firstsurface of the die attach pad are exposed from the first surface of themold structure.
 18. The electronic device of claim 16, furthercomprising a heat sink disposed in thermal communication with the heatspreader pin of the die attach pad.
 19. The electronic device of claim16, where the first through hole technology heat spreader pin comprisesa plurality of heat spreader pins.
 20. The electronic device of claim16, where the first through hole technology heat spreader pin is formedas an integral part of the die attach pad.
 21. A semiconductor package,comprising: a die pad comprising first and second opposite surfaces withone or more through hole technology (THT) heat spreader structuresprotruding through the first surface of the die pad; an integratedcircuit die affixed to the second surface of the die pad; and a moldcompound encasing the integrated circuit die and die pad, leavingexposed the first surface of the die pad and the one or more THT heatspreader structures.
 22. The semiconductor package of claim 21, wherethe one or more THT heat spreader structures are positioned and disposedfor attachment to a printed circuit board.
 23. The semiconductor packageof claim 22, where the one or more THT heat spreader structures arepositioned and disposed for insertion through one or more vias formed inthe printed circuit board.
 24. The semiconductor package of claim 21,where the one or more THT heat spreader structures are formed as anintegral part of the die pad.
 25. The semiconductor package of claim 21,where the one or more THT heat spreader structures are formed as anintegral part of the die pad by etching, milling, punching or machininga lead frame.
 26. The semiconductor package of claim 21, where the oneor more THT heat spreader structures comprises a plurality of heatspreader pins formed integrally to the die pad.
 27. The semiconductorpackage of claim 21, where the die pad comprises: a pad having one ormore mounting holes formed in the first surface; one or more THT heatspreader pins affixed into the one or more mounting holes of the pad sothat the one or more THT heat spreader pins protrude from the pad. 28.The semiconductor package of claim 27, where the one or more THT heatspreader pins are affixed by press fitting, cold welding or insertingthe one or more THT heat spreader pins into the one or more mountingholes.
 29. The semiconductor package of claim 21, where the one or moreTHT heat spreader pins comprise copper.